The McFarland U.S. Pat. No. 3,739,994, issued June 19, 1973, discloses a known deboning machine, in which bony pieces of meat or fish are first ground or chopped in a meat grinder utilizing a screw which presses the pieces against a perforated plate. The pieces are then ground or chopped by rotary blades adjacent the plate. The ground material passes through the perforations in the plate into a separator housing having a generally cylindrical screen with a multitude of small perforations therein. A pressure auger is rotatable within the screen, with close clearance therebetween. The pressure auger develops pressure which presses the meat and other soft materials through the perforations of the screen, while the particles of bone and other hard materials are propelled by the auger to the discharge end of the separator housing from which the hard particles are discharged through restricted orifice formed by an annular valve which maintains pressure in the separator housing.
In another embodiment of the deboning machine, as disclosed in such McFarland patent, the bony meat or fish material is ground separately and is introduced into the separator housing by a food pump, which may be of the rotary vane type.
In the McFarland deboning machine, a filter mat of bone and fibrous particles is formed on the screen, in the clearance space between the screen and the pressure auger, and is effective to filter out small particles of bone and other hard materials. However, due to the initial grinding or chopping of the bony meat or fish material, the ground material contains a fair percentage of small particles of bone and other hard materials. An appreciable percentage of such small particles of bone and other hard materials manages to pass through the filter mat and the perforations with the meat and other soft materials. The presence of the small hard particles in the meat is undesirable.
Thus, the deboning or separating machines of the prior art present the problem of reducing, as much as possible, the percentage of small particles of bone and other hard materials which come out of the machine, mixed with the meat and other soft materials.